One such known method is described in "Electrical conductivities in oil-bearing shaly sands", Waxman M. H. and Smits L. J. M., SPE paper 1863-A presented at 42nd Ann. Fall Meeting, Houston, October 1-4, 1967, hereinafter referred to as the SPE paper.
This publication discloses a method of determining a parameter selected from the electrical conductivity and the volume fraction of a component in a composition comprising a plurality of components, wherein the electrical conductivity of the composition is measured, and a relationship between the conductivity of the composition and the conductivity of a component is selected.
This known method uses the following relationship which is generally referred to as the Waxman-Smits model: EQU C.sub.o =C.sub.w /F*+BQ.sub.v /F*
where C.sub.o =conductivity of fully brine saturated rock
C.sub.w =conductivity of brine present in the formation PA1 F*=a formation factor PA1 B=equivalent conductance of sodium clay-exchange cations as a function of C.sub.w PA1 Q.sub.v =cation exchange capacity per unit pore volume.
The results achieved with this known method are not always sufficiently accurate, probably because of the empirical nature of the Waxman-Smits model which provides a relationship between the earth conductivity and the various other parameters.
It is an object of the invention to provide a more accurate method of determining a parameter selected from the electrical conductivity and the volume fraction of a component in a composition comprising a plurality of components.